Meson: Set _WIN32_WINNT to 0x0601 (Windows 7)

We want to set _WIN32_WINNT so that functions will be properly found in
the headers, to target the NT6.1+ (Windows 7+) APIs.

Also improve the checks for if_nametoindex() and if_indextoname() on
Windows as they are supported in Windows Vista+, but they have
to be checked by linking against iphlpapi.lib (or -liphlpapi).  On other
platforms, they are still checked as they were before.

https://bugzilla.gnome.org/show_bug.cgi?id=783270

config.h.meson

@@ -768,7 +768,7 @@
 /* Define for large files, on AIX-style hosts. */
 #mesondefine _LARGE_FILES
 
-/* Target the Windows XP API */
+/* Target the Windows 7 API */
 #mesondefine _WIN32_WINNT
 
 /* Needed to get declarations for msg_control and msg_controllen on Solaris */

gio/meson.build

@@ -369,7 +369,7 @@ if host_system == 'windows'
   contenttype_sources += ['gcontenttype-win32.c']
   platform_deps += [cc.find_library('shlwapi'),
                     cc.find_library('dnsapi'),
-                    cc.find_library('iphlpapi'),
+                    iphlpapi_dep,
                     winsock2]
   win32_sources += [
     'gwin32registrykey.c',

meson.build

@@ -255,6 +255,11 @@ foreach m : struct_members
   endif
 endforeach
 
+# Windows Support (Vista+)
+if host_system == 'windows'
+  glib_conf.set('_WIN32_WINNT', '0x0601')
+endif
+
 functions = [
   'alloca',
   'mmap',
@@ -311,8 +316,6 @@ functions = [
   'kqueue',
   'kevent',
   'endservent',
-  'if_indextoname',
-  'if_nametoindex',
   'sendmmsg',
   'recvmmsg',
 ]
@@ -328,6 +331,25 @@ else
   have_func_statfs = false
 endif
 
+if host_system == 'windows'
+  iphlpapi_dep = cc.find_library('iphlpapi')
+  iphlpapi_funcs = ['if_nametoindex', 'if_indextoname']
+  foreach ifunc : iphlpapi_funcs
+    if cc.has_function(ifunc,
+                       prefix : '#define _WIN32_WINNT 0x0601\n#include <winsock2.h>\n#include <iphlpapi.h>',
+                       dependencies : iphlpapi_dep)
+      idefine = 'HAVE_' + ifunc.underscorify().to_upper()
+      glib_conf.set(idefine, 1)
+      glib_conf_prefix = glib_conf_prefix + '#define @0@ 1\n'.format(idefine)
+      set_variable('have_func_' + ifunc, true)
+    else
+      set_variable('have_func_' + ifunc, false)
+    endif
+  endforeach
+else
+  functions += ['if_indextoname', 'if_nametoindex']
+endif
+
 # AIX splice is something else
 if host_system != 'aix'
   functions += ['splice']
@@ -674,6 +696,7 @@ endif
 # AC_FUNC_PRINTF_UNIX98
 # Nothing uses HAVE_UNIX98_PRINTF
 
+
 # Check for nl_langinfo and CODESET
 # FIXME: Check for HAVE_BIND_TEXTDOMAIN_CODESET
 if cc.links('''#include <langinfo.h>